Method of making cathode assemblies and products



L kiiea e t; 2a, 1956" A. P. LA ROCQUE 7 2,895,854

METHOD OF MAKING CATHCDE ASSEMBLIES AND PRODUCTS 2 Sheets-Sheet l COAT/N6 COMPRISING CATHODE METAL CARBONATES BONDED BY WATER-SOLUBLE NICKEL BASE 9 con r50 CATHODE BASE 2 3- NICKEL BASE FOR CATHODE RAY TUBES COATING COMPRISING 8 CATHODE METAL CARBON/I TES BONDED BY WATER-SOLUBLE CELLULOSE DERIVATIVE FOR RECEIVING CATHODE BASE} 10 TUBES SUSPENSION OF CATI-IODE METAL CARBONATES IN AN AQUEOUS SOLUTION 0F A! WATER-SOLUBLE CELLULOSE DERIVATIVE MASK 4 I 7 1 Y I \I L I i-\\ 7 NICKEL CA THODE BASES mvemon: ARMAND P. LA ROCQUE ATTYS.'

y 21, 1959 A. P. LA ROCQUE' 2,895,854-

METHOD OF MAKING CATHCDE ASSEMBLiES AND PRODUCTS Filed Sept. 28, 1956 2 Sheets-Sheet 2 ru/vasrav BASE i2 4 wms 004 mm couPn/s/A/a REFRACTORY arms owosn 15 aouaso ar WATER-SOLUBLE CELLl/LOSE DERIVATIVE :Z {conrsa c4 man: 1 HEATER use ARMAND P. LA ROCQUE United States Patent METHOD or MAKING CATHODE ASSEMBLIES AND PRODUCTS H Armand P. La Rocque, Montgomery Township, Pa., as-

signor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania The present invention relates to a novel method for preparing cathode assemblies for electron tubes; and, more particularly, the invention relates to a'method for preparing a cathode assembly for electron tubes, such as cathode ray tubes, radio receiving tubes, television receiving tubes, gas discharge tubes, and the like, comprising an oxide-coated cathode and an insulated oxidecoated cathode heater which method provides many important advantages over prior methods. The invention also relates to a cathode assembly, comprising a coated cathode unit and a coated cathode heater unit, from which the ultimate cathode assembly comprising the ultimate oxide-coated cathode and the ultimate insulated oxidecoated cathode heater can be prepared, and to the coated cathode unit and coated cathode heater unit.

The cathode, or electron emitter, of an electron tube comprises as the cathode unit, a base of nickel containing small amounts of reducing impurities and having a coating of oxides of certain metals, usually of barium and strontium or of barium, strontium and. calcium, thereon. In cathode ray tubes the nickel base of the cathode is usually in the formv of a cup or cap and the coating is placed on the outside'flat surface thereof. In receiving tubes the nickel base is usually in the form of a hollow cylinder and the coating is placed about theperiphery thereof extending to within a predetermined distance from the ends of the cylinder. In applying the oxide coating it has been customary practice first to apply to the portion of the nickel base to be coated a suspension of salts of barium and strontium or of barium, strontium and calcium, in a solution of nitrocellulose in an organic vehicle. The vehicle is usually butyl or amyl acetate diluted with acetone or with an alcohol like'methanol or amyl alcohol. After the suspension has been applied, the coating is dried and the coated cathode-is assembled with the cathode heater, also coated as described below, in cathode assembly form. Electric current is then passed through the heater, generating heat which decomposes the carbonates to oxide form and decomposesthe binder. Much dilficulty has been and is being experienced .with this procedure. It has been found that coatings applied in this manner often crack, and possess pooradherence to the nickel base. This is particularly true where a dense coating is desired, such as in tubes requiring very close cathode grid spacing, like color television'picture tubes. It has been found that this difiiculty is-due pri-' marily to the sensitivity of the organic system to moisture;

7 Patented July 21, 1959 I expensive, and do not fully eliminate the limitations im-* posed by such procedure. In addition to the moisture problem, are: the fire and explosion hazard involved with the use of the flammable materials which in turn require the utmost care and expensive equipment; the expense of the solvents and diluents; the harmful effects of the volatile solvents and diluents on workers, and the problem of controlling the purity and composition of the solvents and diluents.

The cathode heater of an electron tube comprises a fine, high-resistance wire, like tungsten, and generally in the form of a helix and having an electrically insulating coating of refractory oxide thereon. In applying the insulating oxide coating it has been customary practice to apply to the high-resistance wire base a suspension of the refractory oxide in a solution of an organic binder in an organic vehicle. After the suspension has been applied, the coating is dried. When the cathode heater and the cathode are assembled and current passed through the a heater, the heat decomposes the binder. 1

' diluents on workers, and the problem of controlling the It is believed that, during drying of the initial coating,

purity .and composition of the solvents and diluents, referred to above in connection with the cathode unit.

It is the principal object of the present invention to provide an improved method for preparing cathode assemblies for electron tubes.

It is another object of the invention to provide an improved method for making electron tube cathode assemblies, involving preparing a carbonate-coated cathode unit and an insulating oxide-coated cathode heater unit, assembling the cathode unit and the cathode heater unit and passing current through the cathode heater unit heating the heater and cathode units including their respective coatings, which method provides substantial advantages over prior methods.

It is another object of the present invention to provide a method for applying the electron emitting oxide coat ing to a cathode base in the preparation of oxide-coated cathodes for electron tubes whereby cracking and poor adhesion of the coating to the base are eliminated.

Still another object of the present invention is to -pro'- vide a novel method for preparing oxide-coated cathodes for electron tubes which possess improved operating characteristics over oxide-coated cathodes prepared by previous methods.

It is another object of the present invention to provide a method for applying the electrical-insulating, refractory oxide coating to a cathode heater base in the preparation of oxide-coated cathode heaters for electron tubes whereby chipping and poor adhesion of the coating to the base are substantially reduced.

Still another object of the present invention is to provide a novel method for preparing oxide-coated cathodes and electrical-insulating, refractory oxide-coated cathode heaters whereby fire and explosion hazards are elim-t i inated;'fume hazards to Workers-are removed; problem? sembly from which'the cathode assembly canbe prepared,.

the provision of a novel cathode unit from.Which1 the ultimate oxide-coated. cathode may be-prepared and. the provisionof a novel. cathode heater unit fromawhich the oxide-coated cathode heater may be prepared, will be-- come. apparent from a consideration of the following.

specification and claims.

The method of the present invention comprises apply:

ingto the cathode base, a fluid suspension comprising,

trostatic .sprayingmay be used with safety. In addition, it has been found that the carbonate and refractory oxide suspensions are much more stable than the suspensions previously used so that the carbonates and refractory oxides do not settle out, and this is of particular value when automatic spray equipment; such as electrostatic sprayers, is employed. Another important advantage in the use ofthepresent procedure is the ease of control of the barium and strontium carbonates in anaqueous solution of: a'water-soluble cellulose derivative selected from the group consistingof salts-of carboxymethyl cellulose, carboxyrnethylhydroxyethyl cellulose and. salts of carboxymethylhydroxyethyl cellulose said solution being free of metallic'ions known to'be detrimental to emission and drying; the coating; applying to the cathode heater base, afiuid-suspension comprising refractory metal oxide pow der in an aqueous solution of a Water-soluble cellulose derivative selected from the group consisting, of. salts of oarboxyrnethyl cellulose, carboxymethylhydroxyethyl C61? lulose and salts of carboxymethylhydroxyethyl cellulose and drying the coating; assembling the coated cathode.

and coated cathode heater in cathode assembly form, andpassing current through the cathode heater generating.

heat in the assembly and decomposing. the metal carbonates in the cathode coating to oxide form and decomposing; the cellulose derivative in both coatings.

1 The present invention will be more readily understood from a consideration of the drawings in which:

. Fig. l is an enlarged perspective view, partly in section, ofatypicalcoated cathode for cathode ray tubes;.

Fig. 2 is an enlarged perspective view illustratingthe step of applying the coating suspension to one endof. the cathode-base of Figure 1;

Fig. 3 isan enlarged perspective view, partly in section, of a typical coated cathode for receiving tubes;

- Fig. 4 is an enlarged perspective view,.partly in sectiom. of a typical coated cathode heater; and

I Fig. 5 is a vertical sectional view of a cathode assembly. showing a cathode heater ofthe type shown in Fig; 4 mounted in heating relationship within a cathode ofthe' type shown in Fig. 1.

a It has been found that the use of a salt of carboxymethyl cellulose. or of carboxymethylhydroxyethyl cellu-- lose or. carboxymethylhydroxyethyl cellulose itself as binder, in aqueoussolution, in the application of the cathode: salts to the cathode. base and in the application of the insulating, refractory oxide to the cathode heater results in many important unexpected advantages over prior. procedures. In the first place, the wet coatings can be. dried. and baked without danger of cracking. Furthermore, the ultimate oxide coatings are not only free from: cracks, but adhere tenaciously to the underlying metal. The coated units thus possess improved handlingcharacteristics so that the danger of chipping or removing'a portion of .the coating during handling after dryingandup to the time they are assembled and heated. is materially reduced. By using this procedure, even very denseoxide coatings can be produced, making the procedure especially applicable in the preparation of oxide-coated cathodes for tubes requiring very close cathode grid spacing,. such as color television tubes, rectifier tubeshaving'closely' spaced elements, and the like. Themoisture problem, attendingprevious procedures for applying the cathode. coating, is eliminated by the present procedure. Complicated and expensive expedients, such as vacuum equipment, airconditioning and dehumidifiers, need not be employed. Because the present method. relies. upon. the. use of an aqueous system, the fire and explosion hazards accoma panying the: previous. procedure: are" eliminated, as are thmuseaof. vents and. solvent. recovery systems, and elec-v purity and composition of the solvent, namely water, inasmuch. asdistilled water can readily be obtained or produced by: those practicing the. present process. In this way, careful control of materials entering into the ultimate oxide coating can easily be had. Of course, the aqueous system of the present invention presents no fume hazards to workers, as would the volatile solvents and diluents required by the previous procedures. Finally, water is much less expensive than are the organic solvents and diluents previously required;

One: ofthe=moreimportant features of the present invention isthe: discovery; that .the' ultimate oxide coatings provided on the" cathode. possess outstanding. performance characteristics, that i'sactivity and uniformity of emission, over. extendedperiods of. time; This is particularly true whenia sodiumrsaltofxthe cellulose derivative is employed. a The purpose of. the process, of course, is to provide an; ultimatezcoatingof mixed oxides ofbarium and strontium;.on of. barium,.strontiumand'calcium'on the cathode base. andan electrically 'insulatingcoating consisting essentially of refractory oxide on the. cathode heater base. Sincepin the: case of: the: cathode: coating, the. oxides are formed inz situ. through decomposition of carbonates of the stated metals, the'suspensioninitially applied to the cathodes base will" be asuspension of carbonates of the stated metals. The carbonates are normally in co-precipitated. form,. such. as. the: so-called double carbonate in. the: case of-barium' and. strontium and the so-called .triple carbonate: in the case of. barium, strontium and calcium. Tihenuseof-the double. or. triple carbonate results;.upon:1decomposition thereof, in mixed oxide crystals. In the: case; ofthe' cathode heater, the suspension initially applied. to the cathode heater. base will. be a suspension of. the oxide" in powder: form. The. oxide employed will besuch. aswillbei stable: and solidv at the temperatures to which the heater. is subjected during operation, and these mayre'achflOOO-lOO 0, depending upon theparticular device. A. wide variety of metal oxides is available for thisipurpose, forfexample, aluminum oxide, zirconium dioxide, magnesium oxide, silicon dioxide, columbium mono andLdii-oxides,.benylliumoxide, thorium oxide, titaniumdioxide; vanadiumtriand tetra-oxides, and the like. Ofthesesaluminum oxide is preferred.

Referringto the: cellulose derivative that is employed as initial binder for. the cathode. coating and cathode heater coating-inaccordancewith the present invention, it-willlbega's stated; a water-s oluble salt of carboxymethyl cellulose on of carbox-ymethylhydroxyethyl cellulose or carboxymethylhydroxymethyl cellulose itself. Since, as stated previously; thesuspension, especially the suspension applied to the: cathode base, will be free of metal ion'sikn'ownlto be: detrimental to emission, such as zinc, coppen iro'n, lead; bismuth, chromium, gold, silver, mercury and tin-ions, these salts of the cellulose derivatives will not be employed. Other than-these, any'water-soluble' metal, including ammonium, salt of carboxymethyl cellulose .or' of carboxymethylhydroxyethyl cellulose that either completely" decomposes, as does the ammonium salt, or. whose metaldoes. not oxidize or whose metal forms'astable oxide atthe: temperature of the operation of the electron tube,-may--be employed. Of the metal salts,. thos'e'of the alkali: metals, such as sodium, potassium and lithium, and'thoseof the alkaline earth metals, such as calcium;v barium, strontium and magnesium, are preferred; Of theses. the sodium salt is particularly advantageous for reasons setforth hereinabove.

Salts: ofcarboxymgthyl: cellulose are normally prepared by reacting a salt of cellulose, like sodium cellulose, with an acetate, like sodium monochloracetate. The position for substitution of the carboxymethyl groups is not fixed, and substitution may occur at carbons 2, 3 and/or 6 of the anhydroglucose residues. The degree of substitution is governed by the ratio of acetate to salt of cellulose. Since each anhydroglucose unit in a cellulose molecule contains three reactive hydroxyl groups which can be converted to carboxymethyl groups, theoretically complete reaction would mean the introduction of three carboxymethyl groups per anhydroglucose unit providing a degree of substitution of 3. However, the optimum combination of physical properties are generally achieved with a degree of substitution of from 0.3 to about 1.2, the commercial forms of sodium carboxymethyl cellulose having a degree of substitution of about 0.6-0.9.

Carboxymethylhydroxyethyl cellulose may be prepared by reacting cellulose with a hydroxyethylating agent, such as ethylene oxide, preferably in the presence of caustic alkali, and then reacting the product with a carboxymethylating agent, such as chloracetic acid, preferably in the presence of caustic alkali. The mixed cellulose ether generally contains at least about 0.05 hydroxyethyl group and at least about 0.05 carboxymethyl group for each anhydroglucose unit, and the preferred mixed cellulose ethers contain between about 0.15 and about 0.75 hydroxyethyl group and between about 0.2 and about 0.9 carboxymethyl group for each anhydroglucose unit, the total degree of substitution being at least about 0.50 substituents for each anhydroglucose unit. One commercial form of sodium carboxymethylhydroxyethyl cellulose has an average substitution of 0.3 carboxymethyl groups and 0.7 hydroxyethyl groups, and another commercial form has an average substitution of 0.4 carboxymethyl groups and 0.3 hydroxyethyl groups.

The concentration of cellulose derivative in the aqueous solution is relatively immaterial so long as suflicient is present to hold the carbonate or refractory oxide particles, as the case may be, together to each other and to the respective metal bases until the heating operation is completed, and for this purpose the concentration of cellulose derivative should be at least about 0.5%. Although amounts in excess of 5%, by weight, may be employed, no advantage is gained thereby, and preferably the concentration of cellulose derivative in the solution is between about 0.8 and about 3%, by Weight, a concentration of about 1% having been found to be particularly advantageous.

The concentration of the stated cathode metal carbonates or of the refractory oxide in suspension in the respective solutions may vary widely, depending upon the particular means employed for applying the suspension to the cathode and cathode heater bases. For example, when the suspension is applied by dipping, the concentration of the solid particles in the suspension may be very high to the extent where the suspension is in the form of a paste. On the other hand, when the suspension is to be sprayed, the concentration will be relatively low so as to provide a sprayable slurry. With very dilute suspensions, several applications, each of which is followed by drying, may be required.

' The relative proportions of the carbonates in the suspension for application to the cathode base may vary somewhat. Generally, the barium carbonate will range between about 30 and about 70 mole percent and the strontium carbonate will range between about 70 and about 30 mole percent, based on the mixture of carbonates. When calcium carbonate is present, it generally will not exceed about mole percent of the mixture of carbonates.

The suspensions may be applied to the respective bases in a wide variety of ways, including dipping, cataphoresis, spraying, and the like. Of these, dipping and cataphoresis are the most common methods for coating the cathode heater base, and spraying is the most common method for coating the cathode base and in this casea mask may be employed to prevent the suspension from covering those portions of the base to remain uncoated. In this connection, reference may be made to Figure 2 which illustrates one means of application of the suspension to a plurality of cathode bases, for use in cathode ray tubes, by a spraying operation. The numerals 3a represent the cathode bases, 4 represents a mask snugly fitting the ends of the cathode bases, 5 represents the carbonate suspension being directed in spray form toward the upper ends of the cathode bases, 6 represents a conventional spraying device and 7 is a jig for holding the cathode bases during the spraying operation.

After the carbonate suspension has been applied to the cathode base, the coating is dried. This results in a coating comprising the carbonate particles bonded to each other and to the cathode base by means of the cellulose derivative. In this connection, reference may be made to Figures 1 and 3. Figure 1 illustrates a coated cathode base 2 for use in cathode ray tubes. In this case, 1 is the coating and 3 is the base. Figure 3 illustrates a coated cathode base 10 for receiving tubes; 8 being the coating and 9 being the base.

After the refractory oxide suspension has been applied to the cathode heater base, the coating is also dried, resulting in a coating comprising the oxide powder particles bonded to each other and to the cathode heater base by means of the cellulose derivative. In this connection, reference may be made to Figure 4 which illustrates a coated cathode heater base 11, for use in cathode ray tubes. In this case, 13 is the coating and 12 is the base wire.

The coated cathode and coated cathode heater are then' mounted in cathode assembly relationship (that is, with the cathode heater in heating relationship to the cathode; normally the cathode heater is mounted within the cathode) in the electron tube assembly. This is illustrated in Fig. 5 where 11 is a coated cathode heater as shown in Fig. 4 inserted within a cathode 2 of the type shown in Fig. 1. The electron tube assembly is evacuated, and

current is passed through the cathode heater. This generates heat in the cathode heater base and this in turn heats the cathode heater coating, cathode and cathode coating. Generally the temperature reached in the cathode heater coating is at least 1000 C. and may go as high as 1600 C. and in the cathode coating at least 800 C. and may go as high as 1000 C. The cellulose derivative in both coatings is decomposed and the carbonates in the cathode coating are decomposed to oxide form, the decomposition products being removed, under the vacuum, from the system.

The cathode base, as stated, is generally of nickel or a predominately nickel alloy containing a small amount of a reducing impurity or impurities. Generally, the cathode base will consist of at least 95% of nickel with the remainder being a reducing element or elements like silicon,

magnesium, manganese, titanium, tungsten, aluminum and the like. The reducing element or elements activate the cathode causing emission by dilrusing through the nickel and reacting with the oxide of the coating to convert the metal oxides to elemental form.

' pends upon the structure of the particular cathode with which it is used. The cathode heater may be in other forms such as serpentine, loops, spirals or Straight. 7 The present invention will be more readily understood from the consideration of the following specific examples which are given for the purpose of illustration only and are not intended to limit the scope of the invention in any way.

Example I There are dissolved in 136 cubic cm. of pure distilled water 1.36 grams of sodium carboxymethyl cellulose having a D.S. of 0.650.85 and a viscosity in water of 300- 600 cps. at 25 C. at 2% concentration (CMC-70 Medium of Hercules Powder Company). To this solution are added 75 grams of the conventional triple carbonate (Ba, Sr and Ca) cathode mix. The mixture is ball milled for about 15 hours. The resulting slurry is then sprayed to one end of a nickel alloy cathode shank (A-31 alloyed base type of the Superior Tube Company, Norristown, Pa., containing 96% nickel and 4% of tungsten) until a coating .05 mm. thick is built up. The coatingis then dried at 25 C. for 12 minutes.

Six cathode units prepared in this manner are subjected to adherence tests in the followingmanner: Each cathode is mounted, with a cathode heater, on a standard cathode ray stem with a small glass bulb sealed to the stem to complete the assembly. Each cathode is subjected to excessively rapid heating to about 950 C. during which the carbonates are decomposed to oxide form and the cellulose residue decomposed andremoved from the coating. In each case the coating remains intact. This is a vigorous test and coatings applied by prior procedures using organic systems generally fail when subjected to this test.

Six more cathodes prepared in this manner were mounted in triode cathode ray tube guns and sealed in 4 inch CR bulbs. The tubes were processed, aged and tested for activity and useful life in the conventional manner with the results listed below:

1 Tube broken on this test.

With this manner of testing, a cathode activity of 80% or better is considered satisfactory. The above results indicate a high degree of emission and good uniformity of activity over a long period of time.

Example 11 In this example five cathode shanks of P-SO alloy base of Superior Tube Company (99+% of nickel and traces of the usual reducing impurities) are coated as in Example I. Each of these cathodes is placed in a triode cathode ray gun and sealed in 5 inch CR bulbs, and are processed, aged and tested for activity anduseful life with the results given below:

Hours 0 504 720 920 1,472 7 2,650

CATHODE ACTIVITY Average 128. 2 109. 2 97 102. 2 106. 8 110. 8

j 8 Example III In this example six cathode shanks of the type used in xample II are coated as in Example I using as the I coating composition a suspension of 75 grams of the conmains intact.

Example IV With 260 ccs. of a 1%, by weig'ht, solution of sodium carboxymethyl cellulose having a D.S. of 0.65-0.85 and a viscosity in water of 300600 cps. at 25 C. at 2% concentration (CMC-70 Medium of Hercules Powder Company) are mixed gms. of fine aluminum oxide powder.

Cathode heater bases of the type illustrated in Fig. 4 of the drawing, the helix of which has an outer diameter of about 0.1 inch and a length of about 0.3 inch and prepared from tungsten wire having a diameter of .0035 inch, are immersed in the resulting suspension and coated by cataphoresis at about 50 volts. The coated heaters are then removed and placed in a gentle stream of air until the coating is dry.

The resulting coated cathode heaters can be subjected to normal handling, which includes welding heater tabs to the lead wires and inserting the heater into the cathode wherein the helix is flexed and compressed, without danger of chipping the coating.

The same procedure is used when applying coating using carboxymethylhydroxyethyl cellulose and its salts as binders.

Example V A coated cathode heater as prepared in Example IV is inserted in a coated cathode as prepared in the first paragraph of Example I. The assembly is mounted in a standard cathode ray tube, the tube evacuated and current is passed through the cathode heater. The heat generated decomposes the sodium carboxymethyl cellulose in both coatings and the carbonate in the cathode coating, the gaseous decomposition products being withdrawn under vacuum. The resulting assembly is ready for use as a cathode ray tube.

Modification is possible in the selection of cellulose derivatives, amounts thereof and constituents of the coatings as well as in the particular techniques followed Without departing from the scope of the invention.

I claim:

1. In the preparation of cafliode assemblies involving application of a suspension of cathode metal carbonates to a cathode base and drying the coating, application of a suspension of refractory oxide powder to a cathode heater base and drying the coating, assembling the coated cathode heater and cathode in cathode assembly" relationship and passing current through the cathode heater to generate heat to heat the assembly, decomposing the coating binders and the carbonates to oxide form, the improvement which comprises applying said carbonates to said cathode base as a suspension in an aqueous solution of a water-soluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, car-boxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose, said solution being free of metal ions detrimental to emission, and applying said refractory oxide powder as a suspension in an aqueous solution of a water-soluble cellulose derivative selected from the group consisting of salts of carboxy- 9 methyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose.

2. The method of claim 1 wherein the cellulose derivative in each solution is a salt of carboxymethyl cellulose.

3. The method of claim 2 wherein the salt of carboxymethyl cellulose is a sodium salt.

4. In the preparation of oxide-coated cathodes involving application of a suspension of cathode metal carbonates to a cathode base, drying the coating and heating the assembly to decompose the carbonates to oxide form, the improvement comprising applying said carbonates as a suspension in an aqueous solution of a water-soluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose, said solution being free of metal ions detrimental to emission.

5. The method of claim 4 wherein said cellulose derivative comprises a salt of carboxymethyl cellulose.

6. The method of claim 5 wherein said salt of carboxymethyl cellulose is a sodium salt.

7. The method of claim 4 wherein said cellulose derivative comprises carboxymethylhydroxyethyl cellulose.

8. The method of claim 4 wherein said cellulose derivative comprises a salt of carboxymethylhydroxyethyl cellulose.

9. The method of claim 8 wherein said salt of carboxymethylhydroxyethyl cellulose is a sodium salt.

10. The method of claim 4 wherein the concentration of cellulose derivative in said solution is between about 0.5 and about 5%, by Weight.

11. The method of claim 10 wherein the concentration of cellulose derivative is between about 0.8 and about 3%, by weight.

12. The preparation of oxide-coated cathodes which comprises the step of applying to the cathode base a suspension of combined carbonates selected from the group consisting of combined barium and strontium carbonates and combined barium, strontium and magnesium carbonates in an aqueous solution of a water-soluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose, said solution being free of metal ions detrimental to emission.

13. A cathode unit for electron tubes comprising a cathode base having a coating thereon comprising cathode metal carbonate particles bonded to each other and to the cathode base with a water-soluble cellulose derivative selected from the group consisting of salts of canboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose, said coating being free of metals detrimental to emission.

14. The product of claim 13 wherein said cellulose derivative comprises a salt of carboxymethyl cellulose.

15. The product of claim 14 wherein said salt of carboxymethyl cellulose comprises a sodium salt.

16. The product of claim 13 wherein said cellulose derivative comprises carboxymethylhydroxyethyl cellulose.

17. The product of claim 13 wherein said cellulose derivative comprises a salt of carboxymethylhydroxyethyl cellulose.

18. The product of claim 17 wherein said salt of carboxymethylhydroxyethyl cellulose comprises a sodium salt.

19. In the preparation of oxide-coated cathode heaters involving application of a suspension of refractory oxide powder to a cathode heater base wire and drying the coating, the improvement comprising applying said oxide powder as a suspension in an aqueous solution of a watersoluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose.

20. The method of claim 19 wherein said cellulose derivative comprises a salt of carboxymethyl cellulose.

21. The method of claim 20 wherein said salt of carboxymethyl cellulose is a sodium salt.

22. The method of claim 19 wherein said cellulose derivative comprises carboxymethylhydroxyethyl cellulose.

23. The method of claim 19 wherein said cellulose derivative comprises a salt of carboxymethylhydroxyethyl cellulose.

24. The method of claim 23 wherein said salt of carboxymethylhydroxyethyl cellulose is a sodium salt.

25. The method of claim 19 wherein the concentration of cellulose derivative in said solution is between about 0.5 and about 5%, by weight.

26. The method of claim 25 wherein the concentration of cellulose derivative is between about 0.8 and about 3%, by weight.

27. The preparation of oxide-coated cathode heaters which comprises the step of applying to the cathode heater base wire a suspension of aluminum oxide powder in an aqueous solution of a water-soluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose.

28. A cathode heater unit for electron tubes comprising a cathode heater base wire having a coating thereon comprising refractory oxide powder particles bonded to each other and to the cathode heater base wire with a water-soluble cellulose derivative selected from the group consisting of salts of carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and salts of carboxymethylhydroxyethyl cellulose.

29. The coated cathode heater unit of claim 28 wherein said coating is free of metals detrimental to emission.

30. The product of claim 29 wherein said cellulose derivative comprises a salt of carboxymethyl cellulose.

31. The product of claim 30 wherein said salt of carboxymethyl cellulose comprises a sodium salt.

32. The product of claim 29 wherein said cellulose derivative comprises carboxymethylhydroxyethyl cellulose.

33. The product of claim 29 wherein said cellulose derivative comprises a salt of carboxymethylhydroxyethyl cellulose.

34. The product of claim 33 wherein said salt of carboxymethylhydroxyethyl cellulose comprises a sodium salt.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,044 Ruben Dec. 10, 1929 1,977,318 McCullough Oct. 16, 1934 2,070,816 Von Wedel Feb. 16, 1937 2,662,028 Fenton Dec. 8, 1953 FOREIGN PATENTS 669,392 Great Britain Apr. 2, 1952 749,429 Great Britain May 23, 1956 OTHER REFERENCES Hollabaugh et al.: Ind. and Eng. Chem., October 1945, pp. 943-947.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,895,854 July 21, 1959 Armand Pa Le. Rocque It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 57, for "carboxymethylhydroiqymethyl" read carboxy= methylhydroxyethyl column '7, line 8, and column 8, line 19, for "D S of Oo5 Oc85", in each occurrence, read dns, of Ou6 5-=O 85 Signed end sealed this 29th day of March 1960.,

(SEAL) Attest:

ROBERT C, WATSON KARL H, AXLINE Attesting Officer Commissioner of Patents 

1. IN A PREPARATION OF CATHODE ASSEMBLIES INVOLVING APPLICATION OF A SUSPENSION OF CATHODE METAL CARBONATES TO A CHATODE BASE AND DRYING THE COATING, APPLICATION OF A SUSPENSION OF REFRACTORY OXIDE POWDER TO A CATHODE HEATER BASE AND DRYING THE COATING, ASSEMBLING THE COATED CATHODE HEATER AND CATHODE IN CATHODE ASSEMBLY RELATIONSHIP AND PASSING CURRENT THROUGH THE CATHODE HEATER TO GENERATE HEAT TO HEAT THE ASSEMBLY, DECOMPOSING THE COATING BINDERS AND THE CARBONATES TO OXIDE FORM, THE IMPROVEMENT WHICH COMPRISES APPLYING SAID CARBONATES TO SAID CATHODE BASE AS A SUSPENSION IN AN AQUEOUS SOLUTION OF A WATER-SOLUBLE CELLULOSE DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF SALTS OF CARBOXYMETHYL CELLULOSE, CARBOXYMETHYLHYDROXYETHYL CELLULOSE AND SALTS OF CARBOXYMETHYLHYDROXYETHYL CELLULOSE, SAID SOLUTION BEING FREE OF METAL IONS DETRIMENTAL TO EMISSION, AND APPLYING SAID REFRACTORY OXIDE POWDER AS A SUSPENSION IN AN AQUEOUS SOLUTION OF A WATER-SOLUBLE CELLULOSE DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF SALTS OF CARBOXYMETHYL CELLULOSE, CARBOXYMETHYLHYDROXYETHYL CELLULOSE AND SALTS OF CARBOXYMETHYLHYDROXYETHYL CELLULOSE. 